Enantioselective Synthesis of (+)- and (-)-Muricatacin through SE2' Addition of Nonracemic .gamma.-Silyloxy Allylic Stannanes to Aldehydes

Abstract

The acetogenins (R,R)-(+)- and (S,S)-(-)-muricatacin were synthesized through the highly stereo-selective addition of γ-silyloxy allylic stannanes (S)-6 and (R)-6 to (E)-ethyl 3-formylpropenoate (12) in the presence of BF 3 -OEt 2 . The resulting adducts (R,R)-13 and (S,S)-13 afforded the aforementioned acetogenins upon catalytic hydrogenation and subsequent deprotection-lactonization with aqueous HF. Interestingly, additions of stannanes 6 (racemic) to the saturated aldehydes RCH 2 CH 2 CHO (8, R=CO 2 Et, R=CN, R=Cl in the presence of BF 3 -OEt 2 afforded ca. 70:30 mixtures of syn and anti adducts 9a-c. In contrast, the n-alkyl aldehyde 8 (R=n-C 4 H 9 ) underwent highly selective syn addition (97:3) with the crotyl analogue 7 of stannane 6